Technical Advice on Transforming a Character Model into a Monster


I’ve been working on a horror-esque cinematic where a character turns into a monster for the player to fight (similar to Resident Evil). For this sequence, I’m looking to have the character begin as a basic human character, but progressively transform in a sequence. Ideally, I’d like to have the character grow an extra set of arms and a set of spines at various points on the body, but keeping the overall bipedal rig. I don’t think that this kind of transformation would be possible in one fluid motion, so I’ve been planning on doing a series of jump-cuts to zoom in on each transformation. I apologize for the flood of questions, but I haven’t been able to find the correct resources/techniques to accomplish this feat, and I was hoping that that you all would be able to at least point me in the right direction!

For the general body changes, I’ve been experimenting with shape keys, but I’ve been having issues keeping geometry detail as I shape the monster body. For instance, when I try to sculpt new body tone, details such as the belly button stretch and deform more than intended. The below image shows the original model and the poorly sculpted model with the belly button deformed.

Is there a way to mask the sculpt or progressively adapt it such that these details remain usable and scale uniformly from the original model?

For the extra arms, I had tried to duplicate the original body and delete everything from the dupe except for the arms that I wanted to attach. The purpose of this was to retain the shape/weight painting data for the arms that worked well, and join the arms to the body with bridged edge loops and some texture blending. However, when I go to join the dupe’s armature to the original, the duplicate arms reference the original’s rig rather than the dupe’s.

Is there a way to retain the weights and association of the newly joined arms, without re-painting the arms again?

For the transformation sequence, I’d like to have both the arms and the set of spines grow from the skin of the character. I figure that shape keys would be far too complicated, especially for the arms, and I wanted to know if there was a way to have these features seem to extend from the smooth skin. I had initially scaled up the model and scaled down the added arms bone-by-bone such that they were invisible, but that tended to mess with the UVs and it seemed that there was a more versatile solution.
I could probably get away with something like this as long as I keep the character completely clothed, but as the transformation happens I’d intended to have the clothes tear apart, and it seems a bit hard to control/get looking good. This would be the most important part of the transformation sequence, but I haven’t found many resources that accurately address this idea.

Thanks for taking the time to read this! Any advice and/or links to tutorials would be much appreciated, and I’d be interested in hearing your suggestions for approaching a concept such as this.

Thank you!